水文環境變遷與地下水位變化之關係－兼論員山地區缺水問題

1997年五、六月間宜蘭縣員山地區因地下水位下降約2公尺，使當地居民的地下水井因抽不到水，造成生活困擾，並質疑附近金車礦泉水公司抽水所致。地下水位的變化主是受降水或抽地下水的影響；1997-1998年可能受聖嬰現象影響，降水有異常劇烈變動，除天候外是否還有其他因素造成地下水位下降？本文透過地理實察，充份了解水文環境後，以簡單的相關多項分期延滯迴歸模式（polynomial distributed lag regression model）分析地下水位與降水量的相關及降水後對地下水的影響，並以抽水試驗（pumping test）求得地層係數，利用戴西定律（Darcy's law）估算蘭陽沖積扇北岸的地下水流動量約為20x 10^6 m^3/yr，根據當地水文環境分析，以2 mm/day作為安全出水量應屬合理；適度降低地下水位，可增加出水量，也可改善下游地區之洪患及排水不良等問題，亦有利於土地利用。近年來地下水位有下降之趨勢，可能與蘭陽溪疏波、砂石廠開採砂石、水田休耕轉作、農地重劃、涵管引水等因素有關。員山地區地下水位距地面多在3公尺以內，平均導水係數（T）大於2 m^2/min有充分的地下水可供利用，應無缺水之虞。

關鍵字

地下水；降水量；水位；缺水；安全出水量；水文環境

並列摘要

A field study was conducted in Yuan-Shan, I-Lan to determine the cause of water shortage in 1997. It was found that groundwater level was lowered by 2 meters at the time and that it was probably caused by the reduction in precipitation.Fluctuations in groundwater level can be attributed to factors such as precipitation and changes in the hydrologic environment such as river quarrying and the resting of paddy fields. Correlation and polynomial distributed lag regression model were used to analyze the relationship between groundwater and precipitation. Using the Darcy's Law, we were able to ca1culate groundwater flow in the northern alluvial fan in I-Lan to be about 20x 10^6 m^3/yr. Our results suggest that the amount of 2 mm/day is an acceptable safe yield. Lowering groundwater level may reduce flooding and help drainage problems in the downstream areas, facilitating better land use. Since the groundwater level is no more than 3 meters from the ground surface and the average T value is greater than 2 m^2/min, water shortage should not be of concern in the this area.

並列關鍵字

Groundwater ； precipitation ； water table ； water shortage ； safe yield ； hydrologic environment

國際替代計量

水文環境變遷與地下水位變化之關係－兼論員山地區缺水問題

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